Documentation of file format/image publishing process

I don't use a Mac myself, but would like to make several QEMU images that I have created more easily available to Mac users. I currently make them available to Windows and Linux users as Virtualbox-based Vagrant boxes hosted on the Vagrant Cloud (https://app.vagrantup.com/boxes/search), but that's not an option for users with ARM-based Macs.

Is there any documentation of the file format used for .utm images, and how they can be made available via a URL? This would be very helpful for image creators seeking to make their VMs available to Mac users.